Defeat resistant burglar alarm contact



Nov. 10, 1959 A. T. SAWICKI DEFEAT RESISTANT BURGLAR ALARM CONTACT 3 Sheets-Sheet 1 Filed Feb. 13, 1958 Nov. 10, 1959 A. TQSAWICKI DEFEAT RESISTANT BURGLAR ALARM CONTACT 3 heets-Sheet 3 1 Filed Feb. 13, 1958 E W L 9 2 L 6 2 8 7 /l/ 3 3 NT 6 3 3 a &5 2 h! 0 6 L GROUND 4 LINE Unimd States Patent DEFEAT RESISTANT BURGLAR ALARM.

' CONTACT Alfred T. Sawicki, .St. James, N.Y., assignor to American District Telegraph Company, Jersey City, N.J., a corporation of New Jersey Application February 13, 1958, Serial No. 714,985

16 Claims. (CLZOil-S'?) The present invention relates to burglar alarm contacts and more particularly to such contacts of the type used to provide protection for doors, windows and similar building openings.

A number of reliable andefiicient burglar alarm contacts have been developed and are in use in providing electrical protection against intruders using doors, windows and similar openings. Such contacts have been of a number of types including mechanically or magnetically operated contacts which are actuated when a door or window' on whichthey are mounted is opened. For most installations the existing contact constructions are adequate.

However, in certain classes of protection situations a high degree of security is required, this being notably the casein certain government or government sponsored installations. On high security jobs, protection mustbe provided not only from the ordinary intruder who simply forces a door or window but also from the highly trained intruder who is familiar with the protection installation and who is prepared to take steps to defeat the protection. For example, in the case of magnetic contacts, such an intruder may be provided with magnets and shields which will simulate the magnet mounted on a door so that, as the door is opened, the substitute magnet will prevent the contacts from operating to give an alarm.

Moreover, in a'high security installation consideration,

must be given to attempts by persons within the installation to defeat or assist in the defeat of the protection system.

A principal object of the present invention has been to provide a novel and improved burglar alarm contact.

More particularly, it has been an object of the invention to provide a novel and improved burglar alarm contact which isdefeat resistant even against. attack by highly trained persons.

A further object of the invention has been the provision of a novel and improved burglar alarm contact of the magnetic type which is resistant to defeat by the use of magnets, shields, or other devices.

Another object of the invention has been the provision of a burglar alarm contact of the foregoing type which,.upon operation, opens, grounds and opens the burglar alarmv circuit in sequence and which can be used on direct wire, circuit or local alarm protection systems.

A further object of the invention has been the provision of a burglar alarm contact of the foregoing type which aifords a circuit indication of attempts to compromise the system.

Experience has proven that it is foolhardy to refer to any protection device or system as being completely defeat proof, but. the preferred contact construction of the present invention has been subjected to repeated defeat attempsby highly trained engineers thoroughly familiar with burglar alarm systems, and has successfully resisted all such attempts.

Other and furtherobjccts, features. and advantages of the invention will appear from the following description.

2,912,540 Patented Nov. 10, 1959 The burglar alarm contact of the invention comprises a contact element and an actuating element, one of which is mounted on a fixed part of the building opening, for example, adoor frame, and the other of which is mounted on a movable portion of the opening, for example, the door, so as to be adjacent the first element when the opening is in a closed position. The contact element comprises a plurality of spaced magnetically actuable switch elements arranged to be connected to an external alarm circuit. The actuating element comprises a source of a magnetic field arranged so that, when the opening is in its closed position, at least one of the switch elements is subjected to a magnetic field of sufficient intensity to operate the same, and another of the switch elements is subjected to a null of magnetic field indensity cover removed;

Fig. 4 is a rear view showing the terminal side of the contact element block of :Fig. 3, the cover being removed;

Fig. Sis a circuit diagram for the contact element of Fig. 3;

Fig. 6is a perspectiveview of the front or magnet side .of one form of actuating element'block constructed in accordance with the invention;

Fig. 7 is a circuit diagram for a modified form of contact element in accordance with the invention; and

Fig. 8 isaschematic diagram illustrating another modified form of contact element and actuating element construction in accordance withthe invention.

Referring now to the drawings and more particularly to Figs. 1 and 2, a preferred form of the burglar alarm contact'of the invention is shown as comprising a contact element block generally designated 10 and an actuating element block generally designated .11. The contact element block 10 has a base 12 and a cover 13, while the actuating element block has a similar base 14 and a similarcover 15. The bases 12 and 14 are provided with holes adapted to receive screws for mounting. As shown in 'Fig l, the base 12 of the contact element block may be mounted on the door frame 16 with the cover 13 extending perpendicularly away from the door frame. The base .14 of the actuating element block may be mounted at the top of the door 17 adjacent the contact element block and with the cover 15 extending perpendicularly away from the door. The contact and actuating element blocks should be mounted so as to be parallel to each other and in vertical and horizontal alignment when the door is closed, as shown in Figs. 1 and 2.

Referring now to Figs. 3, 4 and 5, the base 12 has mounted thereon upstanding standards 18 and 19 which support upstanding mounting plate 20. The plate 20 is :disposed parallel to the long side of the base 12. The plate 20 is provided with three spaced holes at each end to accommodate mounting posts 21-26. Between eachpair of posts 21-24, 22-25, and 23-26, as shown in Fig. 3, there is suspended at respective one of magnetic switch elements. 27, 28 and 29. i

The switch elements 27, 28 and 29 may be identical in construction and comprise elongated hermetically sealed glass envelopes 30, 31 and 32, and thin flat metal reeds-33, 34 and 35 each mounted at one end thereof in one end of the respective envelopes and extending slightly over half way down the envelopes. Similar thin fiat metal reeds 36, 37 and 38 are mounted at one end thereof in the other ends of the respective envelopes and also extend slightly over half way down the envelopes so that the pairs of reeds 3336, 3437 and 35-38 overlap. The reeds are mounted so that the overlapping ends are free to move toward and away from each other. Electrical contacts are carried from the reed mounting ends, through the envelope ends and through respective spring mounts 3944 to posts 21-26, respectively. The spring mounts serve the dual purpose of providing support for the envelopes and affording electrical contact between the reeds and the posts. While the spring mounts provide a slight resiliency, the envelopes are nevertheless held thereby in fixed positions.

Screws 45 are provided to afiix the plate to the standards 18 and 19. Screw holes are provided in flange portions 46 and 47 of standards 18 and 19 to permit attachment of the cover 13. A gasket 48 may be provided between the base 12 and the cover 13. Looking at the terminal side of the contact element block, as shown in Fig. 4, it will be seen that screws are provided in the posts 22, 24 and for making external electrical connections.

The reeds 3338 are made of a suitable magnetic material such as iron, so that, in the presence of a magnetic field of at least a predetermined strength, the respective reed pairs 3336, 3437 and 35-38 will be attracted together and will afford good electrical contact between the corresponding posts 21-24, 2225 and 23-26. The reed mountings are such that, in the absence of such a magnetic field, the reed pairs will be separated and will not afiord the electrical contact. The magnetic material used for the reeds should not be so soft magnetically that the magnetic fields acting thereon will cause them to stick together because of residual magnetism.

As shown in Fig. 3 and also in Fig. 5, the terminal posts 21 and 23 are connected together and the posts 25 and 26 are connected together. Posts 25 and 24 are connected to the burglar alarm circuit lines L1 and L2, respectively, While the post 22 is connected to ground. The external connecting wires 49 pass out of the cover 13 through an insulating bushing 50, as shown in Fig. 1.

Referring now to Fig. 6, standards 51 and 52 similar to standards 18 and 19 are mounted on the base 14. The standards 51 and 52 are each provided with a pair of spaced spring clips 5356. The spring clips 53 and 55 retain a cylindrical magnet 57 poled as shown, While the spring clips 54 and 56 retain an oppositely poled cylindrical magnet 58. The magnets 57 and 58 are held parallel to each other and in vertical alignment. The disposition of the magnets is such that when the blocks 10 and 11 are aligned, as shown in Figs. 1 and 2, the magnet 57 will be directly opposite the. switch element 27, while the magnet 58 will be directly opposite the switch element 29. As a result, the switch elements 27 and 29 will be closed, as shown in Fig. 5. In Fig. 5, the magnets 57 and 58 are indicated in dotted lines in order completely to illustrate the circuit.

It will be understood that only when the door 17 is closed, or almost closed, will the alignment of the blocks 10 and 11 be adequate to close the switches 27 and 2 The blocks 10 and 11 should be located close to the hinge side of the door 17 (usually about one foot) so that the contact will operate before the door opens appreciablya door opening of about two inches is usually considered safe, but will not operate if the door'is shaken,

as by the wind or a guard.

As explained above, alignment of the blocks 10 and 11 will cause the magnets 57 and 58 to operate the switches 27 and 29, respectively. The switches are operated because the magnetic field emanating from the magnets tends to be concentrated in the low reluctance 4 paths alforded by the reeds 3336 and 35-38, respectively, and, since the overlapping reed ends are free to move, they are urged together by the opposite magnetic poles temporarily established across the gap between the reeds. The switch 28 will not, however, be operated since the opposite poling of the magnets 57 and 58 causes the net magnetic field acting on the reeds 34 and 37 to be substantially zero. Obviously, the simplest arrangement is one in which the switch 28 is located midway between equal strength, oppositely poled magnets, but other arrangements which result in a net magnetic field insuificient to operate the switch 28, may be used.

In operation, with the door closed, the switches 27 and 29 are closed by the magnets 57 and 58, respectively, so that a circuit is completed between lines L1 and L2, this circuit extending from post 25 through a jumper 59, reeds 38 and 35 (switch 29), a jumper 60, and reeds 33 and 36 (switch 27) to post 24. As the door 17 is opened, the-actuating element block 11 starts to move with respect to the contact element block 10. Switch 27 will be the first to be aifected; it will release because the null in magnetic field strength will approach reeds 33 and 36, allowing them to separate to their normal spaced apart condition under the spring action afiorded by their mounting. This opens the circuit between lines L1 and L2.

As the door 17 is opened further, switch 28 will be removed from the magnetic field null and will come under the influence primarily of magnet 58, causing reeds 34 and 37 to contact, closing switch 28. Closing of switch 28 applies ground from terminal 22 to line L1. Switch 29 will remain in the field of magnet 58, and thus will remain operated, until the door has opened sufficiently to release the switch 29. Further opening of the door will release the switch 28 and then the switch 27. When the switch 28 opens, ground is removed from line L1. The opening of switch 27 has no efiect since the L1-L2 circuit was previously opened at switch 27. The

contact of the invention will work equally well on a swinging type door, although, when the door is opened in the opposite direction from that described, the operations of switches 27 and 29 will be interchanged.

The resistance to compromise with which the invention is primarily concerned is achieved through the use of a null in magnetic field intensity acting on one switch and operating magnetic field intensity acting on another switch or switches. Any attempt at compromise by the use of another magnet or magnets or the use of shielding will upset the balance and cause one or more of the switches to operate or release. Thus, if a magnet causes the switch 28 to operate, the lines L1 and L2 will be grounded, giving a ground signal. If a magnet causes either switches 27 or 29 to open, an open signal will' be given.

When the contact is connected to a central station direct wire burglar alarm system, which is the preferred connection, opening of a protected door will first transmit a break signal, followed by a ground and then another break, so that, with the door standing wide open, the central station drop will indicate a double drop of which the ground drop may be reset; the break drop will remain operated until the door is again closed.

A modified contact element block construction is illu trated in Fig. 7. This form of construction employs, instead of the switch 28, a switch 28 which has a fixed normally closed contact 37 in addition to the normally open contacts S it-37. With the protected door closed, the circuit from line L1 to line L2 extends through post 25, reed 37c0ntact 37, post 25, jumper 59, switch 29, jumper 60 and switch 27 to post 24. This construction insures a break before ground in central station connection.

It should be understood that various combinations of switch contacts which open or close upon application of a magnetic field can be employed.

Any suitable materials can be used in the construction of the various parts-ofthecontact--of the invention; 'The bases, mounting plates-andcovers, forexample, could be made of a phenolic plastic. In general; however, magnetic materials should beavoidedexcept for parts included in the magnetic circuits. To-insure proper' operation on metal or metal -claddoors-, the contact element block and actuating element block should be=-spaced-out from the door and frame with non-magnetic spacersi Another modified form of burglar alarm contact construction is illustrated in Fig; 8; Whilethis type of construction is not as defeat resistant asthose of Figs. and 7, nevertheless it affords a substantial improvement over previously used magnetic type contacts: In-Fig. 8, magnetically actuable switches 65" and '66 may be'mounted -on a--door frame so that their" axes are horizontal-but disposed at 90 relative to each other; The switches 65 and 66 may be constructed in the'same way as the switches 27, 28 and 29 of Fig. 3, or one or more of them may be constructed in the same way as the switch 28 of Fig. 7. A magnet 67 is'mounted on the door so that its axis is horizontal and, whenthe door is closed, is parallel to and in vertical alignment with the axis of the switch 66. As the door is moved from its closed position, the magnet moves in a horizontal plane and follows either path shown by the dotted arrows, depending upon.

which way the door opens.

With the door closed, the center of the magnet '67 is disposed directly beneath the intersection of the axes of the switches 65 and 66, and switch 66' will be energized because it lies parallel toandwithin the magnetic field of the magnet 67. Switch 65,. whose axis is at right angles to the axis of the magnet 67 and,whose center is equidistant between the poles of themagnet, will not be, energized since opposite polarities will not be induced onthe opposing contact surfaces and, therefore, no force. will exist tending to pull the contacts together. In other words, the contact areas of the switch 65' lie in an. effective null of the magnetic field. As the magnet is moved to the "left or right inFig. 8 (by movement of the door), the north or south pole of the magnet, as the case may be, will approach closer to the switch6 5"than the other pole, so that the reeds v of, the switch. 65 will be subject to a net magnetic field intensity. As the magnet moves away from the door closed position, thefield intensity acting on. the switch 65 increases, and at. some point will be sulficient to actuate the switch. However, as the magnet moves out from under the switch. 66, the magnetic field intensity acting on the switch 66. will decrease, and at some point this switch will drop out; At some point, the magnet will be sufiiciently removed that both switches will be dropped out. The. circuit connections to the switches v65 and 66 may be. made asfdesired, but will normally provide a break and a ground.

The defeat resistant feature exists. since introducing an external magnetic field will affect switch 65 sooner than switch 66 because switch 65' is. efiectively in a null of magnetic field intensity. To keep switch 66 operated without operating switch 65 would require the external field to be applied at right angles and maintained centralized with respect to switch 65 as. the. door was opened, which would be very difficult.

To provide even greater resistance to attack, amagnetic shield, for example, an iron housing, may be arranged to enclose the contact element block and the actuating element block when the door, window, etc, is closed. Another expedient which may be adopted is to mount the operating parts of the contact and actuating elements at an angle with respect to the door and frame, the angle employed being hidden by the covers. I

Reversal of switch operation may be efiected by mounting a biasing magnet or magnets in association with the contact element block. v f

While the invention has beenfdescribed in connection with specific embodiments thereof and, in a specific use, various modifications thereof will occur to those skilled in inventionas set forth in the appended claims.

What is claimed-is:

1. A burglaralarmcontact'forbuilding openings such as doors, windows and the like, comprising a contact element and an actuating element one ofwhich is mounted on a fixedpart-of the building opening and the other of which is mounted'on a movable portion of said opening so as to beadjacent said one element when said opening is in a closed position, said contact element comprising a plurality of spaced'magnetically actuable switch elements arranged to be connected'to an external alarm circuit, said actuating element comprising a source of a magnetic field arranged so that when saidopeningis in said closed posi-' tion thereof at least one of said switch elements is subjected to a magnetic field-o'f'sutficientintensity to operate the same and another of said switch elements is subjected to a null of magnetic-field intensity insufiicient to operate the same.

2. A burglar alarm contact for building openingssuch asdoors, windows and the like, comprising a contact element mounted on a fixed part of the building opening and an actuating element mounted'on a movable portion of said opening so as to be adjacent said contact element when saidopening is in a closed-position, said contact element comprising a plurality of spaced magnetically actuable switch elements arranged to be connected to an external alarm circuit, saidactuating element comprising a source of a magnetic fieldarranged so that when said openingis in said closed position thereof at least one of said switch elements is subjected to a magnetic field of sufiicient-intensity tooperate thesame and another of'said switchelements is subjected to a null of magnetic field intensity insufiicientto operatethe same.

3. A burglar alarm'contact for building openings such as doors, windowsandth'e like, comprising a contact element and an actuating element one of which is mounted on afixed part ofthe building opening and the other of which is mounted on a movable portion of said opening so as to be adjacent said one element when said opening is in a closed position, said contact element comprising a plurality of spaced magnetically actuable switch. elements arranged to be connected to an external alarm circuit, said actuatingelement comprising a source of a magnetic field arranged so that when said opening is in said closed position thereof at least one of said switch elements is subjected to a magnetic field of sufiicient intensity to operate the same and another of said switch elements is subjected to a null of magnetic field intensity insufiicient to operate the same and so that, as said opening is moved rom said closed position, said other switch element is operated. p p 4. A burglar alarm contact for building openings such as doors, windows and the like, comprising a contact element mounted on a fixed part of the building opening and an actuating element mounted on a movable portion of said opening so as to be adjacent said one element when saidopening is in a closed position, said contact element comprising a plurality of spaced magnetically actuable switch elements arranged to be connected to an external alarm circuit, said actuating element comprising a source of a magnetic'field arranged so that when said opening is in said closed position thereof at least one of said; switch elements is subjected to a magnetic field of suificient intensity to operate the same and another of said switch ing is moved from said closed .position, said other switch element is first operated and then released and said one switch element is released.

5. A burglar alarm contact for buildingopenings such as doors, windows and the like, comprising a contact element and an actuating elementone of which is mounted on a fixed part of the building opening and the other of which is mounted on a movable portion of said opening so as to be adjacent said one element when said opening is in a closed position, said contact element comprising a plurality of spaced magnetically actuable switch elements arranged to be connected to an external'alarm circuit, said actuating element comprising a plurality of magnets arranged so that when said opening is in said closed position thereof at least one of said switch elements is subjected to a magnetic field of sufiicient intensity to operate the same and another of said switch elements is subjected to a null of magnetic field intensity insufficient to operate the same and so that, as said opening is moved from said closed position, said other switch element is first operated and then released.

6. A burglar alarm contact as set forth in claim in which said contact element comprises three parallel magnetically actuable switch elements and said actuating element comprises two magnets each disposed, when said opening is closed, so as to be adjacent to and aligned with a respective one of said switch elements.

7. A burglar alarm contact for doors and the like, comprising a contact element mounted on the fixed frame of the door or the like and an actuating element mounted on the door or the like so as to be adjacent said contact element when said door or the like is in closed position, said contact element comprising three spaced switch elements arranged to be connected in an external electrical protection circuit and each arranged to be operated when subjected to a magnetic field of predetermined intensity, said actuating element comprising a pair of spaced permanent magnets arranged so that when said door or the like is in said closed position thereof one of said magnets is aligned with a first one of said switch elements, the other of said magnets is aligned with a third one of said switch elements and the second one of said switch elements is located in a null of the magnetic field produced by said magnets, the field intensity produced by said magnets being sufiicient to operate said first and third switchrelements and the field intensity in said null being insuificient to operate said second switch element, said second switch element being first operated and then released as said door or the like is moved from said closed position.

8. A burglar alarm contact for doors, comprising a contact element mounted on the fixed frame of the door and an actuating element mounted on the door so as to be adjacent said contact element when said door is in closed position, said contact element comprising three equally spaced parallel switch elements arranged to be connected in an external electrical protection circuit and each arranged to be operated when subjected to a magnetic field of predetermined intensity, said actuating element comprising a pair of spaced permanent magnets arranged so that when said door is in said closed position thereof one of said magnets is aligned with a first one of said switch elements, the other of said magnets is aligned with a third one of said switch elements and the second one of said switch elements is located in a null of the magnetic field produced by said magnets, the field intensity produced by said magnets being sufficient to operate said first and third switch elements and the field intensity in said null being insufficient to operate said second switch element, said second switch element being first operated and then released as said door is moved from said closed position.

9. A burglar alarm contact as set forth in claim 8 in which each of said switch elements is arranged to be electrically open in the absence of a magnetic field of said predetermined intensity.

10. A burglar alarm contact as set forth in claim 8 in which said second switch element affords both an electrically open circuit and an electrically closed circuit in the absence of a magnetic field of said predetermined intensity.

11. A burglar alarm contact for doors, comprising a contact element mounted on the fixed frame of the door and an actuating element mounted on the door so as to be adjacent said contact element when said door is in closed position, said contact element comprising three horizontally aligned, spaced switch elements arranged to be connected in an external electrical protection circuit and each arranged to be operated' when subjected to a magnetic field of predetermined intensity, said actuating element comprising a pair of horizontally aligned, spaced permanent magnets arranged so that when said door is in said closed position thereof one of said magnets is vertically aligned with a first one of said switch elements, the other of said magnets is vertically aligned with a third one of said switch elements and the second one of said switch elements is located in a null of the magnetic field produced by said magnets, the field intensity produced by said magnets being sufficient to operate said first and third switch elements and the field intensity in said null being insufficient to operate said second switch element, said second switch element being first operated and then released as said door is opened.

12. A burglar alarm contact for building openings such as doors, windows and the like, comprising a contact element and an actuating element one of which is mounted on a fixed part ofthe building opening and subjected to a magnetic field of sufficient intensity to operate the same and the other of said switch elements is subjected to a null of magnetic field intensity insuffici'ent to operate the same.

13. A burglar alarm contact as set forth in claim 12 in which said switch elements are disposed substantially 'at'90 relative to each other and said magnet is ar ranged, when said opening is closed, to be parallel to and aligned with said one switch element.

14. A burglar alarm contact for building openings such as doors, windows and the like, comprising a contact element and an actuating element one of which is mounted on a fixed part of the building opening and the other of which is mounted on a movable portion of said opening so as to be adjacent said one element when said opening is in a closed position, said contact element comprising a plurality of spaced magnetically actuable switch elements arranged to be connected to an external alarm circuit, saidswitch elements each comprising a pair of thin strips of magnetic material arranged to contact each other in the presence of a magnetic field intensity of suflicient strength, said actuating element comprising a plurality of magnets arranged so that when said opening is in saidclosed position thereof at least one of said switch elements is subjected to a magnetic field of sufficient intensity to operate the same and another of said switch elements is subjected to a null of magnetic field intensity insufiicient to operate the same.

15. A burglar alarm contact as set forth in claim 14 in which operation of each of said switch elements is adapted to close an electrical circuit and release of each of said switch elements is adapted to open an electrical circuit.

16. A burglar alarm contact as set forth in claim 15 in which operation of one of said switch elements is also adapted to open an electrical circuit.

References Cited in the file of this patent UNITED STATES PATENTS 

